The present invention relates to force transmitting assemblies, and, more particularly, to such assemblies employing toggle bars as force transmitting elements.
There are numerous types of force delivering assemblies which utilize toggles for power transmission. Common among such assemblies are those which are used to exert radial forces between inner and outer objects. One example of such an apparatus is the apparatuses known as internal line-up or alignment clamps which are employed for aligning and holding in alignment adjacent sections of pipe while the pipes are being welded end-to-end. It is well known that pipe sections, particularly larger diameter pipes used in constructing oil and gas transmission lines, are generally out of round or eliptical, particularly at the ends. In order to insure that a proper weld is made between adjacent pipe sections, it is necessary that the abutting pipe ends be forced into alignment as nearly as possible. This pipe alignment is achieved by use of internal line-up clamps which exert a uniform outward force against the interior of the pipe wall. In order to force the pipe into a uniform circular configuration, the forces applied by the clamps must be quite large.
In the usual internal line-up clamps, a toggle linkage is employed between a central assembly and radially movable pipe engaging shoes. The central assembly is movable longitudinally with respect to the pipe while the shoes are movable radially. Thus the shoes can be expanded and retracted into and out of engagement with the walls of the pipe in response to longitudinal movement of the central assembly. Force applied to the central assembly is transmitted through the toggle bars to the shoes. Typical internal alignment clamps are shown in U.S. Pat. Nos. 1,779,649, 2,694,376, 2,906,226, 3,369,725, and 3,462,059. In all of the apparatuses of the above patents, the toggle links are connected by pins about which the toggle links pivot when the line-up clamp expands and retracts. U.S. Pat. No. 4,002,050 shows a force maintaining toggle system in which the toggle elements are pivotally connected by pivot pins or the like.
In all of the above patents, the toggle links are pivotally connected by pins. The pins form load bearing elements, and are in shear when the toggle system is used. Since the pins are the smallest part of the linkage, they are subject to failure as a result of the high shear forces thereon. This result becomes serious in the welding together of adjacent sections of pipe for oil and gas pipelines in that failure of the pins necessitates withdrawal of the clamp to replace the broken pin(s). Additionally, breakage of a pin may cause jamming of the clamp in the pipeline.